The chemical sensitivity of antidromically identified and unidentified preoptic-suprachiasmatic as well as ARC neurons to releasing hormones, steroids, monoamines, cholinergic agents and amino acids was investigated in urethane-anesthetized female rats. Significant differences were observed in the response pattern of identified and unidentified arcuate neurons to dopamine, norepinephrine, acetylcholine and luteinizing hormone-releasing hormone. On the other hand, acetycholine was the only chemical to initiate a significant difference in the response pattern between the identified and unidentified preoptic-suprachiasmatic neurons. Only a single group of neurons, the antidromically identified arcuate neurons, were found to display an excitatory response to leuteinizing hormone-releasing hormone. All ther groups were found to be, for the most part, non-responsive to luteinizing hormone-releasing hormone. BIBLIOGRAPHIC REFERENCES: Kelly, M.J., Moss, R.L., and Dudley, C.A.: The stereospecific changes in the unit activity of preoptic-septal neurons to microelectrophoresed estrogen. To be presented at the Proc. of the Satellite Symposium, Iontophoresis and Transmitter Mechanism in the Mammalian Central Nervous System, Cambridge, England. July, 1977 (Abstr.). Moss, R.L.: Hypothalamic peptides: putative modulators of neural activity. To be presented at the 3rd Brain-Endocrine Interaction Symposium, Wurzburg, Germany, July, 1977 (Abstr.).